1. Field of the Invention
The present invention relates to an absorbent article which is lightweight and yet has a moderate thickness to give users a feeling of assurance against leakage while worn. More particularly, it relates to an absorbent article such as a disposable diaper which is compact in a packaged state but restores its thickness on being taken out of the package for use thereby to make a user feel assured while worn and which maintains moisture permeability. The present invention also relates to an absorbent article such as a disposable diaper which hardly undergoes color change due to ultraviolet rays or nitrogen oxide gas and of which the color change, if any, is invisible from the exterior so as not to impair the appearance.
2. Description of the Related Art
The recent absorbent articles such as disposable diapers and sanitary napkins have been made more compact and easier to carry in packages by improvements added to the structure and the material. However, if absorbent articles such as disposable diapers are made thinner to make the package more compact, the absorbent article lacks stiffness and makes a user feel a fear of leakage during use. Therefore, it has been demanded to develop absorbent articles which are compact and light in their packaged state but restore their thickness when taken out of the package for use thereby giving a user a feeling of assurance while worn.
Japanese Patent Laid-Open Publication No. 51-66194 (corresponding to U.S. Pat. No. 3,916,900) discloses a disposable diaper having an elastic and wet-stable foam layer between an absorbing core and a backing sheet for confining and maintaining the absorbent core in close conformity with the perineal region of the wearer. The foam layer includes urethane foam, vinyl foam, polyvinyl chloride foam, etc. The urethane foam constituting the foam layer is interposed in its orientated state between the backing sheet and the absorbing core (cf. page 5 lower left column, lines 16-19 of the Japanese Publication). The object of the invention disclosed is to confine and maintain the absorbing core in close conformity with the perineal region of the wearer or to establish close elastic conformity of the diaper about the thighs and waist region of the wearer by taking advantage of the elasticity, compressibility, and wet stability of the urethane foam. In other words, this invention doesn""t make use of the compressive recovery of urethane foam with no consideration given to a user""s feeling of assurance.
Japanese Patent Laid-Open Publication No. 3-197128 discloses a three-layered superabsorbent composite structure in which the second layer is a foamed body containing superabsorbent particles. Urethane foam is used as the foamed body. The subject matter of the invention disclosed is incorporation of superabsorbent particles into a foamed body to produce a superabsorbent composite structure (an absorbent body comprising a foamed material). That is, the invention neither aims to make use of the compressive recovery of urethane foam nor to give a user an assuring feeling. Further, the foamed body having a compressive recovery function is hydrophobic. Incorporation of a particulate superabsorbent material into such a hydrophobic foamed body fails to achieve sufficient absorption performance as the structure. It is therefore necessary to separate a material performing an absorption function from a material performing a compressive recovery function.
The urethane foams described in the above cited literature are used neither to utilize their compressive recovery nor to give a user a feeling of assurance in use.
Japanese Patent Laid-Open Publication No. 6-319769 discloses an absorbent article having a baffle made of a liquid impermeable foamed material having a thickness of 0.51 to 1.54 mm and a density of 0.0225 to 0.0962 g/cm3. In this absorbent article, the baffle is not used as a compression recovering sheet but as a liquid impermeable backsheet. Therefore, the article is not to present both compactness when packaged and a feeling of assurance in use. Further, the foamed material is, being cellular (porous), sometimes likely to leak so that it is cannot be said to have necessary functions as a backsheet.
On the other hand, such materials as ink, adhesives, plastics and rubber, generally used in absorbent articles such as disposable diapers and sanitary napkins tend to undergo color change by ultraviolet rays on long-term exposure to sunlight to deteriorate the appearance.
For example, it is known that the urethane foams described in the above literature are yellowed or browned by ultraviolet rays. Where a urethane foam is disposed between a leakproof sheet and an absorbent member, between a topsheet and an absorbent member, inside an absorbent member or in their plural positions of a disposable diaper, etc., only the urethane foam undergoes yellowing to impair the outer appearance when the article is exposed to sunlight for a long period of time or when the article is placed near a fan heater in winter and exposed to nitrogen oxide gas emitted from the fan heater. The yellowed urethane foam is easily perceived particularly in a lightweight disposable diaper of which the members adjacent to the urethane foam, such as the topsheet or the leakproof sheet are made thin. Even where the urethane foam is inside the absorbent member, since a lightweight diaper contains a reduced amount of pulp, the color change will be detected through the adjacent member. Improvement in this respect has therefore been desired. In particular, since the urethane foam described in the 66194/76 supra is a relatively large member in a sanitary napkin, the color change will considerably ruin the appearance of the napkin, giving a user discomfort.
In an attempt to prevent urethane foam from yellowing, it has been suggested to add various stabilizers such as ultraviolet absorbers, antioxidants and piperidine compounds, or to add or apply white pigments such as titanium white. However, these conventional methods are still unsatisfactory in preventing yellowing of urethane foam.
Not only ultraviolet rays but chemical substances, such as nitrogen oxide (NOx) gas, are contributory to the color change. Therefore, the problem of color change cannot be resolved by methods paying attention only to color change by ultraviolet rays.
An object of the present invention is to provide an absorbent article which is thin and compact in a packaged state but restores its thickness on being taken out of the package for use thereby to make a user feel assured while worn.
Another object of the present invention is to provide an absorbent article containing a material susceptible to color change, such as urethane foam, in which the material hardly undergoes color change by ultraviolet rays or NOx gas, or the color change, if any, of the material is invisible from the exterior so as not to impair the appearance.
The above objects are accomplished by an absorbent article comprising a liquid permeable topsheet, a liquid-impermeable and moisture-permeable leakproof sheet, and a liquid retentive absorbent member interposed between the topsheet and the leakproof sheet, wherein a foamed material is disposed between the leakproof sheet and the absorbent member, between the topsheet and the absorbent member, inside the absorbent member or in plural positions thereof, the foamed material having a density of 5 to 35 kg/m3, a no-load thickness of 1 to 10 mm, and a compressive recovery of 60% or more in terms of (b/axc3x97100), wherein a is a thickness (mm) measured after 24-hour standing with no load applied, and b is a thickness (mm) measured after 24-hour compression under a load of 180 gf/cm2 followed by 30-minute standing with no load applied, and the foamed material is fixed at the prescribed position with an adhesive which has been applied to substantially the entire surface of at least one side of the foamed material or substantially the entire contact area of a member to be brought into contact with the foamed material in such a manner that the adhesive is distributed substantially uniformly while providing applied parts and unapplied parts.
The compressive recovery can be measured as follows.
Method of Compressive Recovery Measurement:
The thickness of a foamed material after being allowed to stand for 24 hours under no load (the thickness before compression) is taken as a (mm). The thickness of the foamed material after being compressed under a load of 180 gf/cm2 (17.6 kPa) for 24 hours and then, after the load is removed, allowed to stand for 30 minutes is taken as b (mm). Compression recovery is defined to be b/axc3x97100 (%). Thickness measurement is made with a laser displacement sensor PA-1830, supplied by Keyence Corp., and an average is obtained in a usual manner.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.